Conventional waste paper recycling apparatuses include, for example, the one disclosed in JP 2012-140738A. This is configured as illustrated in FIG. 14.
In FIG. 14, a papermaking unit 13 produces a wet paper 12 from a pulp suspension and has a papermaking wire 43 and a head box 44. The papermaking wire 43 is composed of a mesh belt stretched over a plurality of rollers 42 to move in a conveying direction of the wet paper 12. The head box 44 pours the pulp suspension onto the papermaking wire 43.
The wet paper 12 is dewatered by a dewatering unit 20, which is composed of a felt water absorption belt 47 stretched over a plurality of rollers 46. In the dewatering unit 20, the wet paper 12 is transferred from the papermaking wire 43 to the water absorption belt 47 and the water absorption belt 47 dewaters the wet paper 12 by absorption.
The dewatered wet paper 12 is dried by a drier 14, which has a first conveying belt 51 and a second conveying belt 53. The first conveying belt 51 is a metal belt stretched over a drying roller 49 with built-in heating devices 48 and a plurality of rollers 50. The second conveying belt 53 is a resin mesh belt stretched over a plurality of rollers 52.
In the drier 14, the first conveying belt 51 and the second conveying belt 53 overlap each other across the wet paper 12 on an outer peripheral surface of the drying roller 49 and the drying roller 49 dries the wet paper 12 by heating via the first conveying belt 51.
The wet paper 12 is press dewatered via the water absorption belt 47 and the first conveying belt 51 by a pair of pressing rollers 46a and 50a, which also transfer the wet paper 12 from the water absorption belt 47 to the first conveying belt 51.
The wet paper 12 is dried to produce dry paper 61, which is released from the first conveying belt 51 by a scraper 111 at an outward terminal position of the first conveying belt 51 to be guided to a finishing unit 15.
The finishing unit 15 applies finishing process to the dry paper 61 and delivers recycled paper 62 obtained from the finishing process to a paper holder 63. The finishing unit 15 is provided with a cutting device 60 made of metal to cut the dry paper 61 in a predetermined size and a slitting device 112.
In the above configuration, the pair of pressing rollers 46a and 50a press the water absorption belt 47 and the first conveying belt 51 for dewatering and transfer at the same time. The wet paper 12 sandwiched between the water absorption belt 47 and the first conveying belt 51 is then transferred from the water absorption belt 47 to the first conveying belt 51. After that, at a position away from the position for transferring the wet paper 12, the wet paper 12 is dried by indirect heating with the drying roller 49 having the built-in heating devices 48 via the first conveying belt 51.
Here, compared with a heating temperature for drying that is set for the drying roller 49, the temperature of the first conveying belt 51 at the position for transferring the wet paper 12 is low. The temperature of the wet paper 12 is then raised to the heating temperature for drying after the transfer to the first conveying belt 51.
Accordingly, the wet paper 12 has no concern for sticking to the first conveying belt 51 even when the pair of pressing rollers 46a and 50a strongly press the water absorption belt 47 and the first conveying belt 51.
A large space is however required to secure the paths for the water absorption belt 47 and the first conveying belt 51, interfering with downsizing of the waste paper recycling apparatus.
Meanwhile, when the wet paper 12 is rapidly heated, that is, the wet paper 12 is strongly pressed directly on the heating surface at high temperature of the drying roller 49, the water in the wet paper 12 rapidly vaporizes and expands in a fibrous layer of the wet paper 12 until coming out of the fibrous layer of the wet paper 12, and the thus generated bubbles disturbs the fibrous layer of the wet paper 12, in particular the surface layer of the fibrous layer. As a result, the strength of the dried paper decreases, causing sticking of a thin paper layer to the heating surface.
The present invention has made to solve the above problems, and it is an object thereof to provide a method of drying a wet paper and a waste paper recycling apparatus that achieve downsizing of the apparatus while being capable of drying a wet paper without sticking.